Acoustic physiological monitoring system

ABSTRACT

An acoustic sensor attached to a medical patient can non-invasively detect acoustic vibrations indicative of physiological parameters of the medical patient and produce an acoustic signal corresponding to the acoustic vibrations. The acoustic signal can be integrated one or more times with respect to time, and a physiological monitoring system can determine pulse or respiration parameters based on the integrated acoustic signal. The physiological monitoring system can, for instance, estimate a pulse rate according to pulses in the integrated acoustic signal and a respiration rate according to a modulation of the integrated acoustic signal, among other parameters. Further, the physiological monitoring system can compare the integrated acoustic signal or parameters determined based on the integrated acoustic signal with other signals or parameters to activate alarms.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/636,500, filed Mar. 3, 2015, entitled “Acoustic Pulse AndRespiration Monitoring System,” which is a continuation of U.S. patentapplication Ser. No. 14/206,900, filed Mar. 12, 2014, entitled “AcousticPhysiological Monitoring System,” which claims priority benefit fromU.S. Provisional Application No. 61/780,412, filed Mar. 13, 2013,entitled “Acoustic Pulse And Respiration Monitoring System,” each ofwhich is hereby incorporated herein by reference in its entirety.

BACKGROUND

The “piezoelectric effect” is the appearance of an electric potentialand current across certain faces of a crystal when it is subjected tomechanical stresses. Due to their capacity to convert mechanicaldeformation into an electric voltage, piezoelectric crystals have beenbroadly used in devices such as transducers, strain gauges andmicrophones. However, before the crystals can be used in many of theseapplications they must be rendered into a form which suits therequirements of the application. In many applications, especially thoseinvolving the conversion of acoustic waves into a corresponding electricsignal, piezoelectric membranes have been used.

Piezoelectric membranes are typically manufactured from polyvinylidenefluoride plastic film. The film is endowed with piezoelectric propertiesby stretching the plastic while it is placed under a high-polingvoltage. By stretching the film, the film is polarized and the molecularstructure of the plastic aligned. A thin layer of conductive metal(typically nickel-copper) is deposited on each side of the film to formelectrode coatings to which connectors can be attached.

Piezoelectric membranes have a number of attributes that make theminteresting for use in sound detection, including: a wide frequencyrange; a low acoustical impedance close to water and human tissue; ahigh dielectric strength; a good mechanical strength; and piezoelectricmembranes are moisture resistant and inert to many chemicals.

SUMMARY

Acoustic sensors, such as piezoelectric membranes, can be used todetermine respiration related parameters from an acoustic signal sensedfrom the neck of an individual, such as a medical patient. Thedetermined respiration parameters can include parameters such as theindividual's respiration rate in some implementations. As a result, thesensed acoustic signal can be filtered before signal processing toremove certain frequency components that may not be used to determinethe respiration parameters. In one such embodiment, the sensed acousticsignal can be high-pass filtered to remove or diminish frequencies belowabout 100 Hz and pass frequencies above about 100 Hz because thedetermined respiration parameters may be determined based on frequencycomponents of the sensed acoustic signal that may exceed about 100 Hz.However, such filtering can remove or diminish pulse information thatmay be included in the sensed acoustic signal.

The systems and methods of this disclosure, in some embodiments,advantageously may not high-pass filter a sensed acoustic signal toremove or diminish frequency components below about 100 Hz. Instead, thesensed acoustic signal can be high-pass filtered at a lower frequency,such as about 0.1 Hz, 1 Hz, 10 Hz, 30 Hz, 40Hz, or the like. Thefiltered acoustic signal can be further filtered to remove or reduceeffects on the acoustic signal of a sensing device, which is used tosense and/or process the acoustic signal, to thereby obtain acompensated signal that may correspond closely to a pulse signal of theindividual. The compensated signal can then be used to determinenumerous respiration and pulse parameters, such as the individual'srespiration rate or pulse rate.

Acoustic sensors and associated processing modules that together form asensing device can inherently filter and change signals output by thesensing device. For example, the mechanical properties of an acousticsensor, such as the materials of the acoustic sensor or a match of theacoustic sensor to the skin of an individual, can influence an acousticsignal output by a sensing device. In addition, the electricalproperties of a high-pass, band-pass, or low-pass filter module includedin a sensing device can influence an acoustic signal output by thesensing device. Such filtering and changing of signals, unfortunately,can result in an acoustic signal output by a sensing device that mayhide or mask an underlying physical signal detected by the sensingdevice. The output acoustic signal thus can be difficult to process fordetermining parameters for understanding the physiological condition ofan individual.

The impact of a sensing device, including an acoustic sensor and one ormore associated processing modules, on a detected acoustic signal can beunderstood in terms of a system transfer function. The sensing devicecan be considered to receive an input signal (for example, the vibrationof an individual's skin) and then generate an output signal based onboth the received input signal and a system transfer function. Thesensing system, for instance, may be considered to output a signal thatcorresponds to the input signal after being influenced by the systemtransfer function.

Accordingly, the systems and methods of this disclosure, in someembodiments, can filter an acoustic signal so as to reverse or undo theeffects on the acoustic signal of a sensing device used for sensing orprocessing the acoustic signal. An acoustic signal can be obtained as aresult that corresponds closely to a physical signal detected by thesensing device. This acoustic signal desirably can be understood interms of physical limitations, boundaries, or intuitions since theacoustic signal may correspond closely to a physical signal. Forexample, the acoustic signal can directly correspond to an expansion andcontraction of the sensed skin of an individual, which can be useful indetermining accurate and reliable respiration and pulse parameters forthe individual.

One aspect of this disclosure provides a physiological monitoring systemconfigured to determine one or more pulse or respiration parameters fromone or more of an acoustic signal and a plethysmograph signal. Beforedetermining respiration or pulse parameters from the acoustic signal,the acoustic signal can be integrated one or more times with respect totime. The physiological monitoring system can utilize the integratedacoustic signal to estimate a pulse rate based on pulses in theintegrated acoustic signal and a respiration rate based on modulation ofthe integrated acoustic signal, among other parameters. Thephysiological monitoring system further can compare the determinedparameters with predetermined values or pulse and respiration parametersdetermined based on a plethysmograph signal, for example, to activatealarms of the physiological monitor.

Advantageously, in certain embodiments, the pulse and respirationparameters determined in accordance with this disclosure can increasethe robustness of a physiological monitoring system. For instance, thepulse and respiration parameters can provide one or more additionalparameter values to validate the accuracy of parameters determined usingone or more other physiological sensors. Moreover, the pulse andrespiration parameters determined in accordance with this disclosure canbe sensed closer to an individual's heart or chest than using one ormore other types or placements of physiological sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B are block diagrams illustrating physiological monitoringsystems;

FIG. 1C is a top perspective view illustrating portions of a sensorsystem;

FIG. 2A illustrates an acoustic neck sensor and a chest sensor forphysiological measurements;

FIG. 2B illustrates an acoustic neck sensor and a plethysmograph forphysiological measurements;

FIG. 3 is a schematic diagram of acoustic and optical sensors and sensordrive elements and a corresponding digital signal processor and I/Odrive elements;

FIG. 4 is a block diagram of a pulse and respiration processor of aphysiological monitor that includes an acoustic signal processor and aplethysmograph signal processor;

FIG. 5 is a block diagram of an example acoustic signal processor;

FIG. 6 is a block diagram of an example acoustic filter;

FIG. 7A is an example acoustic signal processed by an acoustic signalprocessor;

FIG. 7B is an example filtered acoustic signal generated by a filter;

FIG. 7C is another example filtered acoustic signal generated by afilter;

FIG. 7D is an example filtered acoustic signal generated by a filterthat illustrates amplitude modulation;

FIG. 8 illustrates a process for determining a patient pulse rate basedon an acoustic signal;

FIG. 9 illustrates a process for detecting an acoustic probe error;

FIG. 10 illustrates a process for determining a patient respiration ratebased on an acoustic signal; and

FIG. 11 illustrates example signals processed by an acoustic signalprocessor.

DETAILED DESCRIPTION

In various embodiments, a physiological monitoring system that includesan acoustic signal processing system can communicate with an acousticsensor to measure or determine any of a variety of physiologicalparameters of a medical patient. For example, the physiologicalmonitoring system can include an acoustic monitor. The acoustic monitormay, in an embodiment, be an acoustic respiratory monitor that candetermine one or more respiratory parameters of the patient, includingrespiratory rate, expiratory flow, tidal volume, minute volume, apneaduration, breath sounds, rales, rhonchi, stridor, and changes in breathsounds such as decreased volume or change in airflow. In addition, insome implementations, the acoustic signal processing system can be usedto monitor or determine other physiological sounds, such as patientheart rate to help with probe off detection, heart sounds (S1, S2, S3,S4, and murmurs), or change in heart sounds including normal to murmuror split heart sounds indicating fluid overload. Moreover, the acousticsignal processing system can further communicate with a second probeplaced over the patient's chest for additional heart sound detection insome implementations.

In certain embodiments, the physiological monitoring system can includean electrocardiograph (ECG or EKG) that may measure or processelectrical signals generated by the cardiac system of a patient. The ECGcan include one or more sensors for measuring the electrical signals. Insome implementations, the electrical signals can be obtained using thesame sensors that may be used to obtain acoustic signals.

In certain embodiments, the physiological monitoring system cancommunicate with one or more additional sensors to determine otherdesired physiological parameters for a patient. For example, aphotoplethysmograph sensor can be used to determine the concentrationsof analytes contained in the patient's blood, such as oxyhemoglobin,carboxyhemoglobin, methemoglobin, other dyshemoglobins, totalhemoglobin, fractional oxygen saturation, glucose, bilirubin, and/orother analytes. In another example, a capnograph can be used todetermine the carbon dioxide content in inspired and expired air from apatient. In yet another example, one or more other sensors, such as apneumotachometer for measuring air flow and a respiratory effort belt,can be used to determine blood pressure, flow rate, air flow, and fluidflow (first derivative of pressure). In certain embodiments, the sensorscan be combined in a single processing system that can process the oneor more signals output from the sensors on a single multi-functioncircuit board.

FIGS. 1A through 1C illustrate example patient monitoring systems,sensors, and cables that can be used to provide acoustic physiologicalmonitoring, such as acoustic pulse and respiration monitoring, of apatient.

FIG. 1A shows an embodiment of a physiological monitoring system 10. Inthe monitoring system 10, a medical patient 12 can be monitored usingone or more sensors 13, each of which can transmit a signal over a cable15 or other communication link or medium to a physiological monitor 17.The physiological monitor 17 can include a processor 19 and, optionally,a display 11. The one or more sensors 13 can include sensing elementssuch as, for example, acoustic piezoelectric devices, electrical ECGleads, pulse oximetry sensors, or the like. The one or more sensors 13can generate respective signals by sensing a physiological condition ofthe patient 12. The signals can then be processed by the processor 19.The processor 19 can communicate the processed signal to the display 11if a display 11 is provided. In an embodiment, the display 11 isincorporated in the physiological monitor 17. In another embodiment, thedisplay 11 is separate from the physiological monitor 17. The monitoringsystem 10 can, for instance, be a portable monitoring system or a pod,without a display, that may be adapted to provide physiologicalparameter data to a display.

For clarity, a single block is used to illustrate the one or moresensors 13 shown in FIG. 1A. It should be understood that the sensor 13shown is intended to represent one or more sensors. In an embodiment,the one or more sensors 13 include a single sensor of one of the typesdescribed below. In another embodiment, the one or more sensors 13include at least two acoustic sensors. In still another embodiment, theone or more sensors 13 include at least two acoustic sensors and one ormore ECG sensors, pulse oximetry sensors, bioimpedance sensors,capnography sensors, or the like. Additional sensors of different typescan also be included. Other combinations of numbers and types of sensorsare also suitable for use with the physiological monitoring system 10.

In some embodiments of the system shown in FIG. 1A, the hardware used toreceive and process signals from the sensors are housed within the samehousing. In other embodiments, some of the hardware used to receive orprocess the signals can be housed within a separate housing. Inaddition, the physiological monitor 17 can include hardware, software,or both hardware and software, whether in one housing or multiplehousings, usable to receive and process the signals transmitted by theone or more sensors 13

As shown in FIG. 1B, the one or more sensors 13 can include a cable 25.The cable 25 can include three conductors within an electricalshielding. One conductor 26 can provide power to a physiological monitor17, one conductor 28 can provide a ground signal to the physiologicalmonitor 17, and one conductor 28 can transmit signals from the one ormore sensors 13 to the physiological monitor 17. For multiple sensorsimplementations, one or more additional cables 115 can further beprovided.

In some embodiments, the ground signal can be an earth ground, but inother embodiments, the ground signal may be a patient ground, sometimesreferred to as a patient reference, a patient reference signal, areturn, or a patient return. In some embodiments, the cable 25 can carrytwo conductors within an electrical shielding layer, and the shieldinglayer can act as the ground conductor. Electrical interfaces 23 in thecable 25 can enable the cable to electrically connect to electricalinterfaces 21 in a connector 20 of the physiological monitor 17. Inanother embodiment, the sensor 13 and the physiological monitor 17communicate wirelessly, such as via an IEEE standard (e.g., IEEE 802,IEEE 802.11 a/b/g/n, WiFi™, or Bluetooth™, etc.)

FIG. 1C illustrates an embodiment of a sensor system 100 including asensor 101 suitable for use with the physiological monitors shown inFIGS. 1A and 1B. The sensor system 100 can include the sensor 101, asensor cable 117, and a connector 105 attached to the sensor cable 117.The sensor 101 can include a shell 102, an acoustic coupler, 103 and aframe 104, which may also be referred to as a sensor support, configuredto house certain componentry of the sensor 101, and an attachmentportion 107 positioned on the sensor 101 and configured to attach thesensor 101 to the patient.

The sensor 101 can be removably attached to an instrument cable 111 viaan instrument cable connector 109. The instrument cable 111 can beattached to a cable hub 120, which can include a port 121 for receivinga connector 112 of the instrument cable 111 and a second port 123 forreceiving another cable. In certain embodiments, the second port 123 canreceive a cable connected to a pulse oximetry or other sensor. Inaddition, the cable hub 120 could include additional ports for receivingone or more additional cables in other embodiments. The hub includes acable 122 which terminates in a connector 124 adapted to connect to aphysiological monitor. In another embodiment, no hub may be provided andthe acoustic sensor 101 can be connected directly to the monitor, via aninstrument cable 111, or directly by the sensor cable 117, for example.Examples of compatible hubs are described in U.S. patent applicationSer. No. 12/904,775, filed on Oct. 14, 2010, which is incorporated byreference in its entirety herein. Examples of acoustic sensors aredescribed in U.S. patent application Ser. No. 14/030,268, filed on Sep.18, 2013, which is incorporated by reference in its entirety herein.

The component or group of components between the sensor 101 and monitorcan be referred to generally as a cabling apparatus. For example, whereone or more of the following components are included, such components orcombinations thereof can be referred to as a cabling apparatus: thesensor cable 117, the connector 105, the cable connector 109, theinstrument cable 111, the hub 120. the cable 122, or the connector 124.It should be noted that one or more of these components may not beincluded, and that one or more other components may be included betweenthe sensor 101 and the monitor to form the cabling apparatus.

In an embodiment, the acoustic sensor 101 includes one or more sensingelements, such as, for example, one or more piezoelectric devices orother acoustic sensing devices. Where a piezoelectric membrane may beused, a thin layer of conductive metal can be deposited on each side ofthe film as electrode coatings, forming electrical poles. The opposingsurfaces or poles may be referred to as an anode and cathode,respectively, Each sensing element can be configured to mechanicallydeform in response to sounds emanating from the patient and generate acorresponding voltage potential across the electrical poles of thesensing element.

The shell 102 can house a frame or other support structure configured tosupport various components of the sensor 101. The one or more sensingelements can be generally wrapped in tension around the frame. Forexample, the sensing elements can be positioned across an acousticcavity disposed on the bottom surface of the frame. Thus, the sensingelements can be free to respond to acoustic waves incident upon them,resulting in corresponding induced voltages across the poles of thesensing elements.

Additionally, the shell 102 can include an acoustic coupler, whichadvantageously can improve the coupling between the source (for example,the patient's body) of the signal to be measured by the sensor and thesensing element. The acoustic coupler can include a bump positioned toapply pressure to the sensing element so as to bias the sensing elementin tension. In one example, the bump can be positioned against theportion of the sensing element that may be stretched across the cavityof the frame. The acoustic coupler further can include a protrusion onthe upper portion of the inner lining, which exerts pressure on thebackbone 110 and other internal components of the sensor 101.

The attachment portion 107 can help secure the sensor assembly 101 tothe patient. The illustrated attachment portion 107 can include firstand second attachment arms 106, 108. The attachment arms can be made ofany number of materials, such as plastic, metal or fiber. Furthermore,the attachment arms can be integrated with the backbone. The undersideof the attachment arms 106, 108 include patient adhesive (for example,tape, glue, a suction device, or the like), which can be used to securethe sensor 101 to a patient's skin. The attachment portion 107 furthercan include a resilient backbone member 110 which may extend into andform a portion of the attachment arms 106, 108. The backbone 110 can beplaced above or below the attachment arms 106, 108, or can be placedbetween an upper portion and a lower portion of the attachment arms 106,108. Furthermore, the backbone can be constructed of any number ofresilient materials, such as plastic, metal, fiber, combinationsthereof, or the like.

As the attachment arms 106, 108 may be brought down into contact withthe patient's skin on either side of the sensor 102, the adhesiveaffixes to the patient, Moreover, the resiliency of the backbone 110 cancause the sensor 101 to be beneficially biased in tension against thepatient's skin or reduces stress on the connection between the patientadhesive and the skin. Further examples of compatible attachmentportions, associated functionality and advantages are described in U.S.application Ser. No. 12/643,939 (the '939 Application), which isincorporated by reference herein. For example, embodiments of attachmentportions are shown in and described with respect to FIGS. 2B, 2C, 9A-9Dand 10 of the '939 Application, which is explicitly incorporated byreference herein in its entirety.

The acoustic sensor 101 can further include circuitry for detecting andtransmitting information related to biological sounds to thephysiological monitor. These biological sounds can include heart,breathing, or digestive system sounds, in addition to many otherphysiological phenomena. The acoustic sensor 101 in certain embodimentsis a biological sound sensor, such as the sensors described herein. Insome embodiments, the biological sound sensor is one of the sensors suchas those described in U.S. patent application Ser. No. 12/044,883, filedMar. 7, 2008, which is incorporated in its entirety by reference herein.In other embodiments, the acoustic sensor 101 can be a biological soundsensor such as those described in the '939 Application. Otherembodiments can include other suitable acoustic sensors. For example, incertain embodiments, compatible acoustic sensors can be configured toprovide a variety of auscultation functions, including live or recordedaudio output (e.g., continuous audio output) for listening to patientbodily or speech sounds. Examples of such sensors and sensors capable ofproviding other compatible functionality can be found in U.S. patentapplication Ser. No. 12/905,036, filed on Oct. 14, 2010, which isincorporated by reference herein in its entirety.

While the sensor system 100 has been provided as one example sensorsystem, embodiments described herein are compatible with a variety ofsensors and associated components.

FIGS. 2A-B illustrate physiological acoustic monitoring system 200embodiments having sensors in communication with a physiological monitor205. As shown in FIG. 2A, a first acoustic sensor 210 can beneck-mounted and utilized for monitoring body sounds and deriving one ormore physiological parameters, such as the pulse or respiration rate ofthe patient 201. An optional second acoustic sensor 220 can be utilizedto monitor body sounds. In an embodiment, the body sound sensor 220 maybe chest-mounted for monaural heart sound monitoring and fordetermination of heart rate. In another embodiment, the second acousticsensor 220 can include an additional body sound sensor mounted proximatethe same body site, but with sufficient spatial separation to allow forstereo sensor reception. As shown in FIG. 2B, an optional plethysmographsensor 230 coupled to the finger of a patient can further be utilizedfor monitoring and deriving one or more physiological parameters, suchas respiration or pulse rate of the patent 201.

FIG. 3 illustrates acoustic 301 and optical 302 sensors and sensor driveelements 303 and a corresponding digital signal processor 340 and I/Odrive elements 304. Some elements in FIG. 3, such as piezoelectricmembrane 317 and optical front-end 325, are denoted as within a dashedarea as optional features and can be included individually or as sets ofelements in some embodiments of physiological monitoring system.

A multi-acoustic sensor configuration 301 can include a power interface313, piezo circuits and a piezoelectric membrane 317 corresponding toeach sensor head 306, 307, The piezoelectric membrane 317 can sensevibrations and generate a voltage in response to the vibrations. Thesignal generated by the piezoelectric membrane can be communicated tothe piezo circuit and transmitted to the monitor 205 (FIGS. 2A-B) forsignal conditioning and processing. The piezo circuit can decouple thepower supply 313 and perform preliminary signal conditioning. In anembodiment, the piezo circuit 316 can include clamping diodes to provideelectrostatic discharge (ESD) protection and a mid-level voltage DCoffset for the piezoelectric signal to ride on, to be superimposed on,or to be added to. The piezo circuit may also, for instance, have a highpass filter to eliminate unwanted low frequencies, such as below about100 Hz for some breath sound applications or below about 30 Hz for somepulse sound applications, and an op amp to provide gain to thepiezoelectric signal, The piezo circuit may also have a low pass filteron the output of the op amp to filter out unwanted high frequencies. Inan embodiment, a high pass filter can be provided on the output inaddition to or instead of the low pass filter. The piezo circuit mayalso provide impedance compensation to the piezoelectric membrane, suchas a series/parallel combination used to control the signal levelstrength and frequency of interest that can be input to the op amp. Inone embodiment, the impedance compensation can be used to minimize thevariation of the piezoelectric element output. The impedancecompensation can be constructed of any combination of resistive,capacitive, and inductive elements, such as RC or RLC circuits.

As shown in FIG. 3, a physiological acoustic monitor 300 embodiment candrive and process signals from the multi-acoustic sensor 301 and theoptical sensor 302. The monitor 300 can include one or more acousticfront-ends 321, 322, an analog-to-digital (A/D) converter 331, an audiodriver 370 and a digital signal processor (DSP) 340. The DSP 340 caninclude a wide variety of data or signal processors capable of executingprograms for determining physiological parameters from input data. Anoptical front-end 325, digital-to-analog (D/A) converters 334 and an A/Dconverter 335 can drive emitters 308 and transform resulting compositeanalog intensity signal(s) from light sensitive detector(s) 309 receivedvia a sensor cable 310 into digital data input to the DSP 340. Theacoustic front-ends 321, 322 and A/D converter 331 can transform analogacoustic signals from piezoelectric elements 301 into digital data inputto the DSP 340. The A/D converter 331 is shown as having a two-channelanalog input and a multiplexed digital output to the DSP. In anotherembodiment, each front-end, can communicate with a dedicated singlechannel A/D converter generating two independent digital outputs to theDSP. An acoustic front-end 321 can also feed an acoustic sensor signal311 directly into an audio driver 370 for direct and continuous acousticreproduction of an unprocessed (raw) sensor signal by a speaker,earphones or other audio transducer 362.

Also shown in FIG. 3, the monitor 300 may also have an instrumentmanager 350 that communicates between the DSP 340 and input/output 360.One or more I/O devices 360 can communicate with the instrument manager350 including displays, alarms, user I/O and instrument communicationports. Alarms 366 may be audible or visual indicators or both. The userI/O 368 may be, as examples, keypads, touch screens, pointing devices orvoice recognition devices, or the like. The displays 364 can beindicators, numeric, or graphics for displaying one or more of variousphysiological parameters or acoustic data. The instrument manager 350may also be capable of storing or displaying historical or trending datarelated to one or more of parameters or acoustic data.

Further shown in FIG. 3, the physiological acoustic monitor 300 may alsohave a “push-to-talk” feature that provides a “listen on demand”capability. For example, a button 368 on the monitor can be pushed orotherwise actuated so as to initiate acoustic sounds to be sent to aspeaker, handheld device, or other listening device, either directly orvia a network. The monitor 300 may also have a “mode selector” button orswitch 368 that can determine the acoustic content provided to alistener, either local or remote. These controls may be actuated localor at a distance by a remote listener. In an embodiment, push on demandaudio occurs on an alarm condition in lieu of or in addition to an audioalarm. Controls 368 may include output filters like on a high qualitystereo system so that a clinician or other user could selectivelyemphasize or deemphasize certain frequencies so as to hone-in onparticular body sounds or characteristics.

In various embodiments, the monitor 300 can include one or moreprocessor boards installed within and used for communicating with a hostinstrument. Generally, a processor board incorporates the front-end,drivers, converters and DSP. Accordingly, the processor board can derivephysiological parameters and communicate values for those parameters tothe host instrument. Correspondingly, the host instrument canincorporate the instrument manager and I/O devices. The processor boardmay also include one or more microcontrollers for board management,including, for example, communications of calculated parameter data orthe like to the host instrument.

Communications 369 may transmit or receive acoustic data or audiowaveforms via local area or wide area data networks or cellularnetworks. Controls may cause the audio processor to amplify, filter,shape or otherwise process audio waveforms so as to emphasize, isolate,deemphasize or otherwise modify various features of the audio waveformor spectrum. In addition, switches, such as a “push to play” button caninitiate audio output of live or recorded acoustic data. Controls mayalso initiate or direct communications.

FIG. 4 is a block diagram of a pulse and respiration processor 400 of aphysiological monitor that can include an acoustic signal processor 410,a plethysmograph (“pleth”) signal processor 420, and a collectionprocessing module 430. The acoustic signal processor 410 can include,for instance, any of the acoustic signal processors described in thisdisclosure. The plethysmograph signal processor 420 includes, forinstance, any of the plethysmograph signal processors described in thisdisclosure. The one or more processors 19 of FIGS. 1A-B and DSP 340 ofFIG. 3 can include the pulse and respiration processor 400.

The pulse and respiration processor 400 can determine one or more pulseor respiration parameters from one or more of an acoustic signal 412 anda plethysmograph signal 422. The acoustic signal processor 410 canreceive an input acoustic signal 412, such as an acoustic signalobtained from the neck of an individual via the first acoustic sensor210 of FIGS. 2A-B or the sensor head 306 of FIG. 3. The acoustic signal412 can correspond to a signal received from the A/D converter 331 ofFIG. 3. The plethysmograph signal processor 420 can receive the inputplethysmograph signal 422, such as a plethysomographic signal obtainedfrom the finger of a patient via plethysmograph sensor 230 of FIG. 2B oroptical sensor 302 of FIG. 3, The plethysomographic signal cancorrespond to a signal received from the A/D converter 335 of FIG. 3.

The acoustic signal processor 410 and plethysmograph signal processor420 can each respectively determine pulse and respiration parameters,such as a pulse rate (“PR”) and respiration rate (“RR”) of a patient.The acoustic signal processor 410 can output 414 the parametersdetermined based on the acoustic signal 412 to the collection processingmodule 430, and plethysmograph signal processor 420 can output 424 theparameters determined based on the plethysmograph signal 422 to thecollection processing module 430. The collection processing module 430can include a decision logic module 430A (sometimes referred to as anarbiter or arbitration module) and a probe error detection module 430B.The collection processing module 430 can perform processing of receivedparameters and output 434 arbitrated parameters for additionalprocessing or detected probe errors, such as for triggering alarmconditions corresponding to the status of a patient.

In some embodiments, the pulse and respiration processor 400 candetermine other pulse or respiration information, such as estimating acarotid intensity or respiration events. Such carotid intensityinformation may be used as an indication of blood pressure changes orpulse variability of an individual. The respiratory events can includeinformation regarding a time when inspiration or expiration begin (Ti orTe, respectively), a time duration of an inspiration or an expiration(Tie or Tei, respectively), a ratio of the time duration of inspirationto expiration, or of expiration to inspiration (Tie/Tei or Tei/Tie,respectively), or some other respiratory event (e.g., conclusion ofinspiration or expiration, midpoint of inspiration or expiration, or anyother marker indicating a specific time within the respiratory cycle, orthe like). Such respiratory event information may be used to furtheridentify the occurrence of various respiratory conditions, such asapnea, occlusion of the breathing passageway, or snoring, for example.

FIG. 5 is a block diagram of the acoustic signal processor 410 accordingto one embodiment. As illustrated, the acoustic signal processor 410 caninclude an acoustic filter 510 and an acoustic signal processing module520, The acoustic filter 510 can filter the acoustic signal 412 toperform an inverse filtering relative to a transfer function of asensing device (for example, including the piezoelectric membrane 317and associated processing circuitry) used to sense the acoustic signalfrom the patient. The acoustic filter 510 can, for instance, perform adeconvolution using the transfer function of the sensing device and theacoustic signal 412 to undo, reverse, or diminish the impact of thesensing device on the acoustic signal 412. In one implementation, wherethe transfer function for a sensing device results in one or morederivatives with respect to time being performed on the detectedacoustic signal, the acoustic filter 510 can integrate the acousticsignal 412 one or more times with respect to time to obtain a filteredacoustic signal 514 corresponding to the carotid pulse of an individual,A sensing device can have a transfer function that results in one ormore derivatives with respect to time being performed on the detectedacoustic signal when, for example, the sensing device may include one ormore high-pass filters, Each high-pass filter in a sensing device canfunction as a differentiator of the acoustic signal. For instance, asensing device may include a piezoelectric membrane, which can functionas a high-pass filter of an acoustic signal, as well as one or morecutoff high-pass filters.

In some embodiments, the transfer function for a particular sensingdevice can be programmed or determined for the acoustic filter 510 atmanufacture, setup-time, or runtime of a physiological monitor. In oneexample, a known input signal, which has an expected output signal, canbe provided to the sensing device at manufacture. By analyzing theactual output signal, expected output signal, and known input signal,the transfer function for the particular sensing device can bedetermined and then stored to a memory of the monitor for laterretrieval. In another example, the outputs of different sensors that maybe connected to the same input signal can be compared at setup-time andused to determine the transfer function. Again, the determined transferfunction can be stored to a memory of the monitor for later retrieval.In other implementations, one or more other approaches additionally oralternatively can be used to determine the transfer function for aparticular sensing device.

The acoustic signal processing module 520 can include a pulse processor520A and respiration processor 520B configured to determine one or morepulse or respiration parameters, respectively, based on the filteredacoustic signal 514. The pulse processor 520A and respiration processor520B can output the determined pulse and respiration parameters 414A,414B for further processing, such as by the collection processing module430 of FIG. 4. In some embodiments, the respiration processor 520B canprocess the filtered signal acoustic signal 514 to determine one or morerespiration parameters, such as respiratory rate, as disclosed in U.S.patent application Ser. No. 14/201,566, filed on Mar. 7, 2014, which isincorporated herein by reference in its entirety.

FIG. 6 is a block diagram of the acoustic filter 510 according to oneembodiment. The acoustic filter 510 can filter the acoustic signal 412in the frequency domain to reverse the effects of a transfer function ofa sensing device used to sense the acoustic signal from the patient. Theacoustic filter 510 can, in one implementation, integrate the acousticsignal 412 one or more times with respect to time to generate thefiltered acoustic signal 514. In some embodiments, the acoustic filter510 can integrate the acoustic signal 412 twice with respect to time toobtain the filtered acoustic signal 514. The filtered acoustic signal514 can advantageously be a signal corresponding to an individual'scarotid pulse and has relatively minimal noise or few other dominatingfrequency components. The filtered acoustic signal 514 can enable thestraightforward determination of numerous characteristics indicative ofpulse or respiration parameters of an individual.

As illustrated in FIG. 6, the acoustic filter 510 can include afrequency domain (“FD”) transform module 610, a filtering module 620,and a time domain (“TD”) transform module 630. The FD transform module610 and TD transform module 630 together can enable performance offiltering by the filtering module 620 in a domain other than the timedomain. Advantageously, in certain embodiments, performing filtering,such as integration, in the frequency domain can reduce the complexityof calculations when performing filtering. For instance, integrating inthe frequency domain can permit integration calculations withoutaccounting for additional constants that may be added if the integrationmay be performed in the time domain.

The frequency domain transform module 610 can receive the input acousticsignal 412 and transform the acoustic signal 412 to generate a frequencydomain equivalent transformed signal 614. In one embodiment, thefrequency domain transform module 610 can perform a fast Fouriertransform (“FFT”) of the acoustic signal 412 to generate the transformedsignal 614. The filtering module 620 can receive the transformed signal614 and, in the case of integration filtering, scale the transformedsignal 614 by a frequency function, such as a function proportional to(2πf)⁻², to generate a scaled signal 624. The filtering module 620 canthus integrate the transformed signal 614 with respect to time in thefrequency domain. The time domain transform module 630 can thentransform the scaled signal 624 to a time domain equivalent filteredacoustic signal 514. In one embodiment, the time domain transform module630 can perform an inverse fast Fourier transform (“IFFT”) of the scaledsignal 624 to generate the filtered acoustic signal 514.

FIG. 7A is a normalized acoustic signal 700, such as the acoustic signal412 of FIGS. 4-6, processed by an acoustic signal processor, such as theacoustic signal processor 410 of FIGS. 4 and 5. The acoustic signal 700can be sensed from the neck of a patient via an acoustic sensor, such asthe first acoustic sensor 210 of FIGS. 2A-B or the sensor head 306 ofFIG. 3. The acoustic signal 700 is shown plotted on an intensity axisversus a time axis. As can be seen in FIG. 7A, the acoustic signal 700can be a relatively chaotic signal, including numerous frequencycomponents ranging from low to high frequency components.

In one implementation, the steps of sensing and processing the acousticsignal 700 from an individual's neck can result in a differentiationwith respect to time of the individual's physiological pulse signal.Accordingly, the acoustic signal 700 can be integrated with respect totime to reverse one or more differentiations during sensing andprocessing. For example, the piezo circuits illustrated in FIG. 3 canoutput a signal corresponding to the derivative of the sensed motion ofthe skin of a patient. Further, before processing the signal at the DSP,a high-pass filter can be utilized and thus output the derivative withrespect to time of the received signals from the piezo circuits. As aresult, advantageously, in certain embodiments, the acoustic signal 700can be filtered by an acoustic filter, such as acoustic filter 510 ofFIGS. 5 and 6, by computing the double integral of the acoustic signalto obtain a signal corresponding to an individual's carotid pulse thatmay have relatively minimal noise or few other dominating frequencycomponents.

FIG. 7B is a normalized filtered acoustic signal 720 generated by afilter, such as the acoustic filter 510 of FIGS. 5 and 6. The acousticsignal 700 of FIG. 7A may have been integrated twice with respect totime to generate the filtered acoustic signal 720. The filtered acousticsignal 720 is shown plotted on an intensity axis versus a time axis. Ascan be seen in FIG. 7B, the filtered acoustic signal 720 can be arelatively ordered signal, including fewer frequency components than theacoustic signal 700 of FIG. 7A.

FIG. 7C is another normalized filtered acoustic signal 740 generated bya filter, such as the acoustic filter of FIGS. 5 and 6. The filteredacoustic signal 740 can be a closer view of the filtered acoustic signal720 of FIG. 7B. The filtered acoustic signal 740 is shown plotted on anintensity axis versus a time axis. Advantageously, in certainembodiments, the filtered acoustic signal 740 can be used by theacoustic signal processing module 520 of FIG. 5 to determine numerouspulse and respiration parameters of an individual.

The filtered acoustic signal 740 can have multiple pulses 742, each witha peak 744 and a valley 746 and extending over a time period 748, wherethe reciprocal of the time period 748 may equal a pulse rate. A carotidindex (CI) value can be defined for each pulse 742:

$\begin{matrix}{{CI} = \frac{AC}{DC}} & (1)\end{matrix}$

where “AC” 752 designates a peak amplitude 744 minus a valley amplitude746 for a particular pulse, “DC” 750 designates a peak amplitude 744relative to a particular intensity level. A pulse variability measurecan be calculated that may be responsive to the magnitude of pulsevariations, such as the amplitude modulation described with respect toFIG. 7D and depicted by envelope 770 of FIG. 7D, for example. One pulsevariability measure can be a pulse variability index (PVI), In anembodiment, PVI is calculated as:

$\begin{matrix}{{PVI} = {\frac{{CI}_{MAX} - {CI}_{MIN}}{{CI}_{MAX}} \times 100}} & (2)\end{matrix}$

where “CI_(MAX)” designates a maximum CI over a particular period oftime and “CI_(MIN)” designates a minimum CI over the particular periodof time. Thus, PVI can be the CI variation, expressed as a percentage ofthe maximum CI. Advantageously, in certain embodiments, pulsevariability measures such as PVI can provide a parameter indicative ofan individual's physical condition or health.

The pulse processor 520A of the acoustic signal processing module 520can analyze the filtered acoustic signal 740 as discussed with respectto FIG. 7C to determine numerous other pulse parameters. In addition todetermining a pulse rate, CI, and PVI, the pulse processor 520A can, forinstance, detect blood pressure changes. Such parameter information canbe useful for determining appropriate doses or timings for delivery ofmedicine to an individual or designing an intelligent cuff inflationsystem for measuring patient blood pressure. Moreover, in certainembodiments, advantageously the parameter information can be based on acarotid signal sensed closer to an individual's heart and with fewerturns in vasculature than a signal sensed from the individual's wrist orfinger, and thus can be useable to determine relatively reliable oraccurate parameter information.

The collection processing module 430 can receive the pulse rate andrelated pulse parameters from the acoustic signal processor 410. Theprobe error detection module 430B of the collection processing module430 can use the parameters, for example, to determine a sensor or probeconnection state including a probe-off, probe-error, or probe-on state,such as discussed with respect to FIG. 9, Further, the collectionprocessing module 430 can use the pulse rate and other pulse parametersand available information to determine a pulse wave transit time (PWTT),corresponding to the blood pressure of an individual. Advantageously, incertain embodiments, by using the filtered acoustic signal 740 andanother signal from an acoustic sensor near an individual's heart, PWTTcan be determined with greater robustness and accuracy than using someother methods. The filtered acoustic signal 740 and the signal from theanother sensor can provide signals in the fluid domain that may notintroduce domain conversion delay. For instance, if PWTT may bedetermined using an ECG signal, the determined PWTT value can include adomain transition delay time for a bodily electrical signal to transferto the individual's muscles.

FIG. 7D is a filtered acoustic signal 760 that illustrates amplitudemodulation. Inhalation and exhalation can create positive pressure andnegative pressure, respectively, on an individual's blood vessels, whichmay modulate the individual's pulse signal. Under certain conditions, anindividual's respiration can amplitude modulate (“AM”) 762 an acousticsignal, such as filtered acoustic signal 720 of FIG. 7B, sensed from theneck of the individual. In particular, the modulation period 764 can beinversely related to the individual's respiration rate. Certainimplementations may utilize other modulations of the acoustic signal,such as a frequency modulation, to determine the respiration rate inplace of or in addition to amplitude modulation.

In some embodiments, respiration rate can be determined in the frequencydomain by analyzing the spectrum of the filtered acoustic signal 760. Inthe frequency domain, the filtered acoustic signal 760 can include atleast a peak corresponding to the pulse rate and two respiration peaksidebands, displaced on either side of the pulse rate peak. Byextracting the respiration beak sidebands, the respiration ratecorresponding to the two respiration peaks can be determined.

In some embodiments, respiration rate can be determined in the timedomain based on the respiration modulation period 764. A time domaincalculation may be based upon envelope detection of the filteredacoustic signal 760, such as a curve-fit to the peaks (or valleys) ofthe filtered acoustic signal 760 or, alternatively, the peak-to-peakvariation. Related measurements of variation in a plethysmographenvelope are described, for instance, in U.S. patent application Ser.No. 11/952,940, filed Dec. 7, 2007, which is incorporated by referencein its entirety herein.

In some embodiments, the respiration processor 520B of FIG. 5 candetermine local maxima 766 and minima 770 in the upper envelope 762 ofthe filtered acoustic signal 760. The maxima 766 and minima 770 cancorrespond to, or may be further processed to determine, variousrespiratory events, such as the onset of inspiration Ti 766, the onsetof expiration Te 770, the duration of inspiration Tie 768, the durationof expiration Tei 772, the ratio of the duration of inspiration toexpiration Tie/Tei, the ratio of the duration of expiration toinspiration Tei/Tie, respiration rate, or other respiration-relatedevents.

FIG. 8 illustrates a process 800 for determining a patient pulse ratebased on an acoustic signal, such as the acoustic signal 700 of FIG. 7A.For convenience, the process 800 is described in the context of thesignals, systems, and devices of FIGS. 2A-B, 3-6, and 7A-D, but mayinstead be implemented by other signals, systems, and devices describedherein or other computing systems.

At block 805, an acoustic signal can be received from a probe. Theacoustic signal can be a signal obtained from the neck of a patient viathe probe, such as the first acoustic sensor 210 of FIGS. 2A-B or thesensor head 306 of FIG. 3. The acoustic signal 412 can correspond to asignal received from the AID converter 331 by the DSP 340 of FIG. 3 orthe acoustic signal 412 received by the acoustic signal processor 410 ofFIGS. 4 and 5.

At block 810, the received acoustic signal can be integrated twice withrespect to time. The integration can be performed by the DSP 340 or theacoustic filter 510 of FIGS. 5 and 6. In some embodiments, theintegration can be performed by the acoustic filter 510 in the frequencydomain as discussed with respect to FIG. 6.

At block 815, a pulse rate can be estimated based on the integratedacoustic signal. The DSP 340 or acoustic signal processor 410 canestimate the pulse rate based on the reciprocal of the time periodbetween pulses of the integrated acoustic signal, such as time period748 of FIG. 7C.

Although block 810 can include the operation of integrating the receivedacoustic signal twice with respect to time in some embodiments, theoperation at block 810 can include one or more other filteringoperations (for example, differentiating, integrating, multiplying,subtracting, or computing the results of another function) in otherembodiments to reverse or undue changes to the received acoustic signaldue to the probe, as well as one or more associated processing modules.

FIG. 9 illustrates a process 900 for detecting an acoustic probe error.For convenience, the process 900 is described in the context of thesignals, systems, and devices of FIGS. 2A-B, 3-5, and 7A-D, but mayinstead be implemented by other signals, systems, and devices describedherein or other computing systems.

At block 905, an acoustic signal can be received from a probe, and aplethysmograph signal can be received from a pleth sensor. The acousticsignal can be a signal obtained from the neck of a patient via theprobe, such as the first acoustic sensor 210 of FIGS. 2A-B or the sensorhead 306 of FIG. 3. The acoustic signal 412 can correspond to a signalreceived from the A/D converter 331 by the DSP 340 of FIG. 3 or theacoustic signal 412 received by the acoustic signal processor 410 ofFIGS. 4 and 5. The plethysmograph signal can be a signal obtained fromthe finger of a patient via a non-invasive sensor, such as theplethysmograph sensor 230 of FIG. 2B or optical sensor 302 of FIG. 3.The plethysomographic signal can correspond to a signal received fromthe AID converter 335 by the DSP 340 of FIG. 3 or the plethysmographsignal 422 received by the plethysmograph processor 420 of FIG. 4.

At block 910, the received acoustic signal can be integrated twice withrespect to time. The integration can be performed by the DSP 340 or theacoustic filter 510 of FIGS. 5 and 6, In some embodiments, theintegration can be performed by the acoustic filter 510 in the frequencydomain as discussed with respect to FIG. 6.

At block 915, a pulse rate can be estimated based on the integratedacoustic signal and the plethysmograph signal. The DSP 340 or acousticsignal processor 410 can estimate the pulse rate PRA based on thereciprocal of the time period between pulses of the integrated acousticsignal, such as time period 748 of FIG. 7C. The DSP 340 orplethysmograph signal processor 420 can estimate the pulse ratePR_(pleth) using the plethysmograph processor 422.

At block 920, the pulse rate PRA can be compared to a pulse rate valueof zero or about zero beats per minute. The DSP 340 or probe errordetection module 430B can perform the comparison. In response todetermining that the pulse rate equals zero or about zero, at block 925,the DSP 340 or combining module 430 can activate an alarm conditionindicating a probe error. For instance, the DSP 340 can transmit asignal to the instrument manager 350 of FIG. 3 to activate an alarm 366of one of the I/O devices 360.

At block 930, the pulse rate PRA can be compared to a first thresholdpulse rate value. The DSP 340 or probe error detection module 430E canperform the comparison. The first threshold value can be a valuedetermined based on a minimum pulse rate that would be expected for anindividual. In some embodiments, the first threshold can equal 20 beatsper minute. In response to determining that the pulse rate does notexceed the first threshold, at block 925, the DSP 340 or combiningmodule 430 can activate an alarm condition indicating a probe error. Forinstance, the DSP 340 can transmit a signal to the instrument manager350 to activate an alarm 366 of one of the I/O devices 360.

At block 935, the difference between the pulse rate PRA and pulse ratePR_(pleth) can be compared to a second threshold pulse rate value. Thesecond threshold value can be a value determined based on a minimumpulse rate difference that would be expected between an acoustic andplethysomographic determined pulse rate. In some embodiments, the secondthreshold can equal 5 or 10 beats per minute. In response to determiningthat the difference exceeds or equals the second threshold, at block925, the DSP 340 or combining module 430 can activate an alarm conditionindicating a probe error. For instance, the DSP 340 can transmit asignal to the instrument manager 350 to activate an alarm 366 of one ofthe I/O devices 360.

At block 940, a no-probe-error state can be determined. For instance,the DSP 340 or combining module 430 can determine that probe may beoperating without error and may take no corrective action. In someembodiments, the DSP 340 or combining module 430 can utilize the absenceof a probe error to determine the validity of a pulse rate or to causeDSP 340 or combining module 430 to output a particular value for displayto a patient.

In some embodiments, other approaches can be additionally oralternatively used to determine probe errors or activate alarms based onthe integrated acoustic signal. For instance, the timing or shape offeatures of the integrated acoustic signal can be compared to featuresof one or more other signals, such as signals from a plethysomographicsensor or another acoustic sensor. The features can include local maximaor minima of the signals, and the like. Deviations in the timing orshape between features of the integrated acoustic signal and features ofthe other signals can indicate a probe error or alarm condition. Asanother example, detected energy levels in lower frequencies of theintegrated acoustic signal can be used to determine the presence of apulse rate and thus to indicate a no probe error state. In a furtherexample, the integrated acoustic signal can be compared to one or moresignal templates to determine whether the integrated acoustic signal hasan expected form, When the integrated acoustic signal does not have anexpected form, a probe error indication can be triggered and an alarmcan be activated. Such other approaches are described in more detail inU.S. patent application Ser. No. 14/137,629, filed Dec. 20, 2013, whichis incorporated by reference in its entirety herein.

Although block 910 can include the operation of integrating the receivedacoustic signal twice with respect to time in some embodiments, theoperation at block 910 can include one or more other filteringoperations (for example, differentiating, integrating, multiplying,subtracting, or computing the results of another function) in otherembodiments to reverse or undue changes to the received acoustic signaldue to the probe, as well as one or more associated processing modules.

FIG. 10 illustrates a process 1000 for determining a patient respirationrate based on an acoustic signal, such as the acoustic signal 700 ofFIG. 7A. For convenience, the process 1000 is described in the contextof the signals, systems, and devices of FIGS. 2A-B, 3-5, and 7A-D, butmay instead be implemented by other signals, systems, and devicesdescribed herein or other computing systems.

At block 1005, the acoustic signal can be received from a probe. Theacoustic signal can be a signal obtained from the neck of a patient viathe probe, such as the first acoustic sensor 210 of FIGS. 2A-B or thesensor head 306 of FIG. 3. The acoustic signal 412 can correspond to asignal received from the A/D converter 331 by the DSP 340 of FIG. 3 orthe acoustic signal 412 received by the acoustic signal processor 410 ofFIGS. 4 and 5.

At block 1010, the received acoustic signal can be integrated twice withrespect to time. The integration can be performed by the DSP 340 or theacoustic filter 510 of FIGS. 5 and 6. In some embodiments, theintegration can be performed by the acoustic filter 510 in the frequencydomain as discussed with respect to FIG. 6.

At block 1015, a respiration rate can be estimated based on theintegrated acoustic signal. For instance, the DSP 340 or acoustic signalprocessor 410 can estimate the respiration rate based on amplitudemodulation of the integrated acoustic signal as discussed with respectto FIG. 7D.

Although block 1010 can include the operation of integrating thereceived acoustic signal twice with respect to time in some embodiments,the operation at block 1010 can include one or more other filteringoperations (for example, differentiating, integrating, multiplying,subtracting, or computing the results of another function) in otherembodiments to reverse or undue changes to the received acoustic signaldue to the probe, as well as one or more associated processing modules.

FIG. 11 illustrates example signals processed by an acoustic signalprocessor. The signals include a raw acoustic signal 1102, such as theacoustic signal 412 of FIGS. 4-6, processed by the acoustic signalprocessor 410 of FIGS. 4 and 5. The raw acoustic signal 1102 can besensed from the neck of a patient via an acoustic sensor, such as thefirst acoustic sensor 210 of FIGS. 2A-B or the sensor head 306 of FIG.3. The acoustic signal 1102 is shown plotted on an intensity axis versusa time axis. As can be seen in FIG. 11, the acoustic signal 1102 can bea relatively chaotic signal, including numerous frequency componentsranging from low to high frequency components.

The signals of FIG. 11 further include a compensated acoustic signal1106 that can be a filtered acoustic signal generated by a filter, suchas the acoustic filter 510 of FIGS. 5 and 6. In one implementation, theraw acoustic signal 1102 may have been integrated twice with respect totime to generate the compensated acoustic signal 1106. As can be seen,the compensated acoustic signal 1106 can be a relatively ordered signal,including fewer frequency components than the raw acoustic signal 1102.

In addition, the signals of FIG. 11 include a high frequency acousticsignal 1104 and a low frequency acoustic signal 1108. The high frequencyacoustic signal 1104 can illustrate just the high frequency componentsof the compensated acoustic signal 1106, and the low frequency acousticsignal 1108 can just illustrate the low frequency components of thecompensated acoustic signal 1106 (for example, the low frequencycomponents between about 0.2 Hz and 0.8 Hz).

Advantageously, in certain embodiments, the low frequency acousticsignal 1108 can be used to accurately and precisely determine one ormore respiration parameters for a patient since the local maxima andminima of the low frequency acoustic signal 1108 can directly correspondto exhalation and inhalation. Multiple consecutive local maxima ormultiple consecutive local minima can thus be correctly identified asmultiple exhalations or multiple inhalations. As a result, an acousticsignal processor can, for example, determine a time when inspiration orexpiration begin (Ti or Te, respectively), a time duration of aninspiration or an expiration (Tie or Tei, respectively), a ratio of thetime duration of inspiration to expiration, or of expiration toinspiration (Tie/Tei or Tei/Tie, respectively) with greater confidence.

Embodiments have been described in connection with the accompanyingdrawings. However, it should be understood that the figures are notdrawn to scale. Distances, angles, etc. are merely illustrative and donot necessarily bear an exact relationship to actual dimensions andlayout of the devices illustrated. In addition, the foregoingembodiments have been described at a level of detail to allow one ofordinary skill in the art to make and use the devices, systems, etc.described herein. A wide variety of variation is possible. Components,elements, and/or steps can be altered, added, removed, or rearranged.While certain embodiments have been explicitly described, otherembodiments will become apparent to those of ordinary skill in the artbased on this disclosure.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. Thus, such conditional language is not generally intended toimply that features, elements and/or states are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or states are included or are to beperformed in any particular embodiment.

Depending on the embodiment, certain acts, events, or functions of anyof the methods described herein can be performed in a differentsequence, can be added, merged, or left out altogether (e.g., not alldescribed acts or events are necessary for the practice of the method).Moreover, in certain embodiments, acts or events can be performedconcurrently, e.g., through multi-threaded processing, interruptprocessing, or multiple processors or processor cores, rather thansequentially.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein can be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. The described functionalitycan be implemented in varying ways for each particular application, butsuch implementation decisions should not be interpreted as causing adeparture from the scope of the disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein can be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor can be a microprocessor, but in thealternative, the processor can be any conventional processor,controller, microcontroller, or state machine. A processor can also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The blocks of the methods and algorithms described in connection withthe embodiments disclosed herein can be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module can reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, a hard disk, a removabledisk, a CD-ROM, or any other form of computer-readable storage mediumknown in the art. An exemplary storage medium is coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium can beintegral to the processor. The processor and the storage medium canreside in an ASIC. The ASIC can reside in a user terminal. In thealternative, the processor and the storage medium can reside as discretecomponents in a user terminal.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the devices or algorithms illustrated can be madewithout departing from the spirit of the disclosure. As will berecognized, certain embodiments of the inventions described herein canbe embodied within a form that does not provide all of the features andbenefits set forth herein, as some features can be used or practicedseparately from others. The scope of certain inventions disclosed hereinis indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1-20. (canceled)
 21. A physiological monitoring system configured tonon-invasively detect acoustic vibrations indicative of one or morephysiological parameters of a medical patient, the physiologicalmonitoring system comprising: one or more hardware processors configuredto: receive an acoustic signal from an acoustic sensor, the acousticsensor configured to attach to a medical patient, detect acousticvibrations associated with the medical patient, and generate theacoustic signal indicative of the acoustic vibrations, wherein theacoustic sensor is associated with a transfer function that affects theacoustic signal generated by the acoustic sensor; process the acousticsignal to lessen an effect of the transfer function on the acousticsignal and generate a processed acoustic signal, wherein the processedacoustic signal corresponds to a scaled frequency domain equivalent ofthe acoustic signal; estimate a physiological parameter of the medicalpatient based at least on the processed acoustic signal, wherein thephysiological parameter includes one or more respiratory or cardiacparameters; and cause a display to display an indication of thephysiological parameter.
 22. The physiological monitoring system ofclaim 21, wherein to process the acoustic signal, the one or morehardware processors configured to scale the acoustic signal by afrequency function.
 23. The physiological monitoring system of claim 22,where the frequency function comprises a function that is proportionalto (πf)⁻².
 24. The physiological monitoring system of claim 21, whereinto process the acoustic signal, the one or more hardware processorsconfigured to integrate a frequency domain equivalent of the acousticsignal with respect to time in the frequency domain.
 25. Thephysiological monitoring system of claim 21, wherein to process theacoustic signal, the one or more hardware processors configured tocompute a double integral with respect to time of the acoustic signal.26. The physiological monitoring system of claim 21, wherein to processthe acoustic signal, the one or more hardware processors are furtherconfigure to generate a frequency domain equivalent of the acousticsignal.
 27. The physiological monitoring system of claim 26, wherein togenerate the frequency domain equivalent, the one or more hardwareprocessors are configured to compute a Fourier transform of the acousticsignal.
 28. The physiological monitoring system of claim 27, wherein theFourier transform comprises a fast Fourier transform.
 29. Thephysiological monitoring system of claim 21, wherein to process theacoustic signal, the one or more hardware processors are furtherconfigured to generate a time domain equivalent of the acoustic signal.30. The physiological monitoring system of claim 29, wherein to generatethe time domain equivalent of the acoustic signal, the one or morehardware processors are configured to compute an inverse Fouriertransform of the acoustic signal.
 31. The physiological monitoringsystem of claim 21, wherein to lessen the effect of the transferfunction on the acoustic signal comprises removing the effect of thetransfer function on the acoustic signal.
 32. The physiologicalmonitoring system of claim 21, wherein the transfer function of theacoustic sensor corresponds to a high-pass filter.
 33. The physiologicalmonitoring system of claim 21, wherein at least a portion of thetransfer function of the acoustic sensor is caused by at least one of aprocessing circuitry of the acoustic sensor, a piezoelectric membrane ofthe acoustic sensor, or a sensed motion of skin of the medical patient.34. The physiological monitoring system of claim 21, wherein thephysiological parameter comprises at least one of pulse rate, expiratoryflow, tidal volume, minute volume, apnea duration, breath sounds, rales,rhonchi, stridor, air volume, airflow, heart sounds, or change in heartsounds.
 35. A method for determining one or more physiologicalparameters of a medical patient, the method comprising: receiving anacoustic signal from an acoustic sensor attached to a medical patient,the acoustic sensor configured to detect acoustic vibrations associatedwith the medical patient and generate the acoustic signal indicative ofthe acoustic vibrations, wherein the acoustic sensor is associated witha transfer function that affects the acoustic signal generated by theacoustic sensor; processing the acoustic signal to lessen an effect ofthe transfer function on the acoustic signal and generate a processedacoustic signal, wherein the processed acoustic signal comprises ascaled frequency domain equivalent of the acoustic signal; estimating aphysiological parameter of the medical patient based at least on theprocessed acoustic signal, wherein the physiological parameter includesone or more respiratory or cardiac parameters; and causing a display todisplay an indication of the physiological parameter.
 36. The method ofclaim 35, wherein said processing comprises integrating a frequencydomain equivalent of the acoustic signal with respect to time in thefrequency domain.
 37. The method of claim 35, wherein said processingcomprises computing a double integral with respect to time of theacoustic signal.
 38. The method of claim 35, wherein said processingcomprises: generating a frequency domain equivalent of the acousticsignal by computing a fast Fourier transform of the acoustic signal; andgenerating a time domain equivalent of the acoustic signal by computingan inverse fast Fourier transform of the acoustic signal.
 39. Aphysiological monitor comprising: an input configured to receive anacoustic signal from an acoustic sensor, the acoustic sensor configuredto attach to a medical patient, detect acoustic vibrations associatedwith a medical patient, and generate the acoustic signal indicative ofthe acoustic vibrations, wherein the acoustic sensor is associated witha transfer function that affects the acoustic signal generated by theacoustic signal; and one or more hardware processors in communicationwith the input and configured to: process the acoustic signal to lessenan effect of the transfer function on the acoustic signal and generate aprocessed acoustic signal, wherein to process the acoustic signal, theone or more hardware processors are configured to scale a frequencydomain equivalent of the acoustic signal, estimate a physiologicalparameter of the medical patient based at least on the processedacoustic signal, wherein the physiological parameter includes one ormore respiratory or cardiac parameters, and cause a display to displayan indication of the physiological parameter.
 40. The physiologicalmonitor of claim 39, wherein to process the acoustic signal, the one ormore hardware processors are further configured to: generate thefrequency domain equivalent of the acoustic signal by computing a fastFourier transform of the acoustic signal; and generate a time domainequivalent of the acoustic signal by computing an inverse fast Fouriertransform of the acoustic signal.